System, method and apparatus employing tones and/or tone patterns to indicate the message type in wireless sensor networks

ABSTRACT

A system and method for operating a wireless network provides for sending a wakeup tone, periodically waking up from a sleep mode to listen for the wakeup tone, upon receiving the wakeup tone, listening for at least one second tone, the at least one second tone being one of (i) a tone in a frequency different from the wakeup tone and (ii) a pattern of tones including at least one frequency different from the wakeup tone, and upon receiving the at least one second tone, performing an action based on the at least one second tone.

FIELD OF THE INVENTION

The present invention relates to a system, method and apparatusemploying frequency tones and/or tone patterns to indicate the messagetype in wireless sensor networks.

BACKGROUND INFORMATION

In wireless sensor networks, to save energy the nodes may perform aradio-frequency (RF) wakeup procedure, in which during a majority of thetime the nodes are in a power down mode, and in which, periodically, thenodes wake up to sample the wireless channel for any signal, and if asignal is present they remain in an active mode to receive the message.In this regard, the signal may followed by a message, the type of whichindicates the action or actions that are required to be performed by theawakened node after the wakeup, and in certain instances it may beessential that the type is known correctly by the awakened node beforethe actual packet exchange. Since a node may be simultaneously awakenedby multiple nodes in the network, there is a chance that interferenceand/or collisions may occur.

SUMMARY OF THE INVENTION

According to an exemplary embodiment and/or exemplary method of thepresent invention, a particular type of tone, or a pattern of tones, issent after the wakeup tone and before any packet exchange to indicatethe particular action or actions that are required to be performed bythe awakened node. Here, for example, the particular frequency of thetone may indicate a type of the message. In this way, the awakened nodemay determine the message type even when there are multiple transmitterssending at the same time.

An exemplary embodiment of the present invention is directed to a methodof operating a wireless network, the method including sending a wakeuptone, periodically waking up from a sleep mode to listen for the wakeuptone, upon receiving the wakeup tone, listening for at least one secondtone, the at least one second tone being one of (i) a tone in afrequency different from the wakeup tone and (ii) a pattern of tonesincluding at least one frequency different from the wakeup tone, andupon receiving the at least one second tone, performing an action basedon the at least one second tone.

Another exemplary embodiment of the present invention is directed to amethod of operating a wireless network, in which the at least one secondtone indicates a message type.

Yet another exemplary embodiment of the present invention is directed toa method of operating a wireless network, in which the action includesat least one of receiving a first message, sending the wakeup tone toanother node in the wireless network and transmitting a second message.

Still another exemplary embodiment of the present invention is directedto a method of operating a wireless network, in which the second messageincludes a sensor reading.

Yet another exemplary embodiment of the present invention is directed toa method of operating a wireless network, in which the wakeup tone issent simultaneously by more than one node of the wireless network.

Still another exemplary embodiment of the present invention is directedto a method of operating a wireless network, in which the at least onesecond tone includes a tone transmitted from each of at least two nodesof the wireless network.

Yet another exemplary embodiment of the present invention is directed toa method of operating a wireless network, in which the at least onesecond tone includes a first tone and a second tone transmittedsimultaneously, the first tone being transmitted by a first node and thesecond tone being transmitted by a second node.

Still another exemplary embodiment of the present invention is directedto a method of operating a wireless network, in which the at least onesecond tone includes a first pattern of tones and a second pattern oftones transmitted simultaneously, the first pattern being transmitted bya first node and the second pattern being transmitted by a second node.

Yet another exemplary embodiment of the present invention is directed toa method of operating a wireless network, in which the first pattern isdifferent from the second pattern.

An exemplary embodiment of the present invention is directed to awireless network, which includes a receiver node that includes anarrangement to receive a plurality of tones each at a predefinedfrequency, an energy storage arrangement, and a control arrangement tooperate the receiver node in a sleep mode to conserve energy, thereceiver node being configured to periodically wake up from the sleepmode to listen for a wakeup tone, and upon receiving the wakeup tone,listening for at least one second tone, the at least one second tonebeing one of (i) a tone in a frequency different from the wakeup toneand (ii) a pattern of tones in at least one frequency different from thewakeup tone.

Another exemplary embodiment of the present invention is directed to awireless network, in which the receiver node further includes anarrangement to perform an action based on the at least one second tone.

Yet another exemplary embodiment of the present invention is directed toa wireless network, in which the receiver node includes at least one ofa sensor and an actuator.

Still another exemplary embodiment of the present invention is directedto a wireless network, which includes at least one transmitter node totransmit the wakeup tone and the at least one second tone.

Yet another exemplary embodiment of the present invention is directed toa wireless network, in which the at least one transmitter node includesat least two transmitter nodes, at least one of which transmits thewakeup tone, and each of which simultaneously transmit at least onefurther tone distinct from one another to collectively form the at leastone second tone received by the receiver node.

Still another exemplary embodiment of the present invention is directedto a wireless network, in which the at least two transmitter nodesinclude a first transmitter node that transmits the at least one furthertone as a single tone at a first predefined frequency, and a secondtransmitter node that transmits the at least one further tone as asingle tone at a second predefined frequency different from the firstpredefined frequency.

Yet another exemplary embodiment of the present invention is directed toa wireless network, in which the at least two transmitter nodes includea first transmitter node that transmits the at least one further tone asplurality of tones in a first pattern, and a second transmitter nodethat transmits the at least one further tone as a plurality of tones ina second pattern different from the first pattern.

Still another exemplary embodiment of the present invention is directedto a wireless node, which includes a power storage arrangement, and anarrangement to receive a plurality of tones each at a predefinedfrequency, the wireless node being configured to periodically listen fora wakeup tone, and upon receiving the wakeup tone, listening for atleast one second tone, the at least one second tone being one of (i) atone in a frequency different from the wakeup tone and (ii) a pattern oftones that includes at least one frequency different from the wakeuptone.

Still another exemplary embodiment of the present invention is directedto a wireless node, which includes an arrangement to perform an actionbased on the at least one second tone.

Yet another exemplary embodiment of the present invention is directed toa wireless node, in which the at least one second tone includes a firsttone and a second tone transmitted simultaneously, the first tone beingtransmitted by a first node and the second tone being transmitted by asecond node.

Still another exemplary embodiment of the present invention is directedto a wireless node, in which the at least one second tone includes afirst pattern of tones and a second pattern of tones transmittedsimultaneously, the first pattern being transmitted by a first node andthe second pattern being transmitted by a second node.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary wireless node, which operates according toalternating sleep and wake cycles.

FIG. 2 shows an exemplary wakeup schedule for an energy constrained nodeof a wireless sensor network.

FIG. 3A shows an arrangement of exemplary nodes of an exemplary wirelessnetwork, and how the exemplary nodes might communicate messages to oneanother.

FIG. 3B shows an exemplary schedule to wakeup the exemplary nodes ofFIG. 3A, and how the exemplary schedule effects the transmissions ofmessages between the nodes.

FIG. 4 shows an exemplary embodiment to use a type tone.

FIG. 5 shows an exemplary embodiment to use a pattern of tone toindicate a message type.

FIG. 6 shows an exemplary method for operating a wireless network.

DETAILED DESCRIPTION

A wireless sensor network may be defined, for example, as a distributedsystem of nodes/motes each equipped with a radio transceiver, amicrocontroller and one or more sensors and/or actuators. The nodes insuch a network may be small and inexpensive, and consequently theresources provided with each node may be necessarily limited. Forexample, the wireless nodes of a network may be equipped with a limitedenergy source, in particular, the wireless nodes may bebattery-operated.

FIG. 1 shows an exemplary wireless node 100, which operates according toalternating sleep and wake cycles. The exemplary wireless node 100includes a radio transceiver 101, a sensor and/or actuator 102, amicrocontroller 103 and a battery 104. The radio transceiver 101 enablesthe exemplary wireless node 100 to send and/or receive wirelesstransmissions. The sensor and/or actuator 102 senses a condition, and/oractuates a movement of an element. The microcontroller 103 controls theradio transceiver 101 and the sensor and/or actuator 102, or otheraspects of the exemplary wireless node 100. The battery 104 providesenergy to power the components of the exemplary wireless node 100.

The design of a wireless sensor network for energy constrained nodes maybe dictated by longevity concerns. One approach to increase thelongevity of a wireless sensor network with energy constrained nodes isto use a sleep schedule where the nodes operate in a low-power or sleepmode for most of the time, periodically waking up to check for activity.

FIG. 2 shows an exemplary wakeup schedule for an energy constrained nodeof a wireless sensor network, in which the node operates in the sleepmode most of the time, and which periodically wakes up for a brief timeperiod to take a sample.

Channel Sniffing and Wakeup

The nodes in a wireless network may wake up from time to time and scoutthe channel for activity. This may be performed, for example, bylistening to the channel for a very short period of time and measuringthe received signal strength. If the signal strength exceeds apredetermined threshold, the node may remain awake in an attempt toreceive a possible transmission, otherwise the node may power itselfdown to conserve energy. Such a process is sometimes referred to as“sniffing the channel”.

The length of the sniffing period and the energy consumed whileperforming a wakeup may determine the longevity of the network. Inpractice, the sniffing length is determined, at least in part, byseveral hardware limitations such as the warm up time of the radio, andthe minimum time required to reliably detect a signal in the channel.The sniffing period may be on the order of hundreds of micro-seconds toa few milliseconds.

Wakeup Schedule

The time at which each node in the network “sniffs” the channel may bedetermined by a wakeup schedule. Here, for example, the wakeup schedulemay be deterministic or random. Moreover, the wakeup schedule may alsobe different for one or more nodes of the network. In this regard,having differing schedules may provide different delay guarantees forthe messages in the network.

FIGS. 3A and 3B show exemplary nodes A through H of an exemplarywireless network 300, and an exemplary schedule 301 to wakeup theexemplary nodes A through H. In particular, FIG. 3A shows how theexemplary nodes A through H of the exemplary wireless network maycommunicate with each other. For example, FIG. 3A shows the following:node A can communicate directly with nodes B and C; node B cancommunicate directly with nodes D and E; node C can communicate directlywith nodes A, D and E; node D can communicate directly with nodes B, C,F and G; node E can communicate directly with nodes B, C, F and G; nodeF can communicate directly with nodes D, E and H; node G can communicatedirectly with nodes D, E and H; and node H can communicate directly withnodes F and G. Such a relationship is shown in FIG. 3A by shaded arrowsbetween the nodes.

FIG. 3A also shows (via a dashed line) the transmission of a messagefrom node A to node H, and the transmission of a message from node H tonode A. In particular, the message transmitted from node A to node H isfirst transmitted from node A to node B, and then transmitted from nodeB to node D, and then transmitted from node D to node F, and thentransmitted from node F to node H. Similarly, but not in identicalfashion, the message transmitted from node H to node A is firsttransmitted from node H to node G, and then transmitted from node G tonode D, and then transmitted from node D to node B, and then transmittedfrom node B to node A. Here, it is noted that the path of the twotransmitted messages between nodes A and H is different, although notrestricted as such.

FIG. 3B shows an exemplary wakeup schedule 301 for each of the exemplarynodes A through H. Here, a square box represents the time at which theparticular exemplary node samples the channel. In this regard, anunfilled white square box indicates that at the sample time there was noactivity to be performed by the exemplary node and therefore theexemplary node immediately returned sleep, while a filled black squarebox indicates that at the sample time there was an activity (e.g.,message transmission and/or receipt) to be performed, and therefore theexemplary node stayed awake to perform the activity.

FIG. 3B also shows (via dashed lines) the wakeup sequence timingrequired for the transfer of the messages depicted in FIG. 3A. Here, thefirst dashed line representing the wakeup sequence timing required forthe message transferred from node A to node H first intersects a sampleperiod for node A, and thereafter intersects the next sample period fornode B, and thereafter intersects the next sample period for node D, andthereafter intersects the next sample period for node F, and thereafterintersects the next sample period for node H. The second dashed linerepresenting the wakeup sequence timing required for the messagetransferred from node H to node A first intersects a sample period fornode H, and thereafter intersects the next sample period for node G, andthereafter intersects the next sample period for node D, and thereafterintersects the next sample period for node C, and thereafter intersectsthe next sample period for node A.

It is noted, for example, with respect to FIG. 3B that the two dashedlines intersect the same sampling period for node D. This represents anexample scenario where node D is awakened by two different nodes for twodifferent reasons. That is, node D is awakened by node B to pass along amessage to node F, and, at the same time, node D is awakened by node Gto pass along a message to node C.

Message Type

As demonstrated above, a node in the network may be awakened fordifferent reasons and by different nodes in the network. According toone exemplary embodiment, the type of the message that follows thewakeup tone may determine the actions that need to be performed by theawakened node after the wakeup.

Determining the type of the message may be essential in many cases, andmay change the way the message is received and/or decoded by the node.Depending on the application scenario, the type of the message mayinclude transmitter information (e.g., who has awakened the node), themessage route (e.g., who the node should forward the message to), thedata content or packet length (e.g., what size of packet should the nodeexpect), or even the priority level of message (e.g., how important themessage is). For example, the type of the message may indicate themessage route, so that the node knows that for the next step which ofits neighbors should be awakened. Another example is the case ofmessages from mobile nodes. Messages from mobile nodes may have adifferent format and/or may be on a different frequency channel.

It is noted, for example, that a node may be awakened at the same timeby multiple nodes for multiple purposes. For example, a mobile node andstationary node may awaken a node at the same time. It may be essential,therefore, that the node determine why it has been awakened even when itis simultaneously awakened by multiple nodes.

Using the Type Tone after the Wakeup Tone

According to an exemplary embodiment of the present invention, a “typetone” (or more generally a pattern of type tones) is transmittedimmediately after the wakeup tone to indicate the type of the messageand essentially the reason that the node has been awakened.

FIG. 4 shows an exemplary embodiment of using a type tone. A transmittersends a wakeup tone (at the time that the receiver is sampling thechannel) in the wakeup frequency, and shortly thereafter the transmitterfollows the wakeup tone with the “type tone”. According to an exemplaryembodiment, the frequency on which the type tone is sent indicates thetype of the message.

At the receiver side, the node samples the channel (in the wakeupfrequency) regularly and/or periodically. If a high signal is detected,the node stays in the receive mode and switches to different frequenciesand samples different tone frequencies. In FIG. 4, for example, the nodesamples three different frequencies, each of which corresponds to adifferent message type. In this way, the receiver can determine the typeof the message. Essentially, the presence of a high signal in apre-specified frequency channel is used to communicate the type of themessage to the receiver.

An advantage of using the type tone after the wakeup tone is itsresilience to a collision condition. Since the receiver only checks thesignal power, the collision of different transmitters may not have anyeffect on the signal. That is, if two nodes send two tones at the sametime, the received power is only increased at the receiver.Additionally, if the node is awakened by multiple nodes for differentmessage types, the node may detect all the different types and then actaccordingly based on the priority level assigned to different messagetypes.

Pattern of Tones

According to another exemplary embodiment, instead of using a singletone, a pattern of tones in different frequencies may be used toindicate different message types. Such an exemplary method may behelpful when there are many different types.

FIG. 5 shows an exemplary embodiment of using a pattern of tone toindicate a message type. Here, the pattern is a sequence of two typetones, each of which is selected from three possible tones. Thereceivers sample for the three possible frequencies during each toneperiod. Hence, a total of 3×3=9 different types is provided using thisexemplary model. By increasing the length of the tone pattern theprobability of false wakeups may be reduced. That is, the probabilitythat noise or interference awaken the node and create a correct messagetype pattern.

As can be seen in FIG. 5, the exemplary embodiment of the presentinvention allows a node to simultaneously receive messages from multiplenodes of the network without collisions occurring. That is, with theexemplary method of the present invention, messages receivedsimultaneously by a node may be easily distinguished.

A Combined Approach

FIG. 6 shows an exemplary method 600 for operating a wireless network.In this regard, the wireless network may be, for example, a network likethe exemplary wireless network 300 shown in FIG. 3A. The exemplarymethod 600 is described as follows.

In step S601, a wakeup tone is sent a node in the wireless network. Inthis regard, the node may be, for example, a wireless sensor node and/oran actuator node, which may or may not be constrained as to a certainresource (e.g., a battery-operated node). In particular, the node may beselected, for example, from one or more the exemplary nodes A through Hshown in FIG. 3A. Moreover, the wakeup tone may be sent exclusively by asingle node of the wireless network, or alternatively, the wakeup tonemay be sent simultaneously by more than one node of the wirelessnetwork.

In step S602, the node is periodically woken up from a sleep mode tolisten for the wakeup tone. Here, for example, the node may be woken upaccording to a particular schedule, such as the exemplary wakeupschedule 301 shown in FIG. 3B.

In step S603, upon receiving the wakeup tone, the node listens for atleast one second tone, the at least one second tone being one of (i) atone in a frequency different from the wakeup tone and (ii) a pattern oftones including at least one frequency different from the wakeup tone.Here, for example, the at least one second tone may indicate a messagetype. In this regard, the at least one second tone may include tonessent exclusively by a single node of the wireless network, oralternatively, the at least one second tone may includes tonestransmitted from each of at least two separate nodes of the wirelessnetwork. For example, the at least one second tone may include a firsttone and a second tone transmitted simultaneously, the first tone beingtransmitted by a first node and the second tone being transmitted by asecond node. In this regard, the at least one second tone may include,for example, a first pattern of tones and a second pattern of tonestransmitted simultaneously, the first pattern being transmitted by afirst node and the second pattern being transmitted by a second node.Moreover/still, the first pattern may be different from the secondpattern

In step S603, upon receiving the at least one second tone, the nodeperforms an action based on the at least one second tone. Here, forexample, the action may include receiving a message, sending the wakeuptone to another node in the wireless network and/or transmitting amessage (e.g., a message that includes a sensor reading).

1. A method of operating a wireless network, the method including:sending a wakeup tone; periodically waking up from a sleep mode tolisten for the wakeup tone; upon receiving the wakeup tone, listeningfor at least one second tone, the at least one second tone being one of(i) a tone in a frequency different from the wakeup tone and (ii) apattern of tones including at least one frequency different from thewakeup tone; and upon receiving the at least one second tone, performingan action based on the at least one second tone.
 2. The method of claim1, wherein the at least one second tone indicates a message type.
 3. Themethod of claim 1, wherein the action includes at least one of receivinga first message, sending the wakeup tone to another node in the wirelessnetwork and transmitting a second message.
 4. The method of claim 3,wherein the second message includes a sensor reading.
 5. The method ofclaim 1, wherein the wakeup tone is sent simultaneously by more than onenode of the wireless network.
 6. The method of claim 1, wherein the atleast one second tone includes a tone transmitted from each of at leasttwo nodes of the wireless network.
 7. The method of claim 6, wherein theat least one second tone includes a first tone and a second tonetransmitted simultaneously, the first tone being transmitted by a firstnode and the second tone being transmitted by a second node.
 8. Themethod of claim 6, wherein the at least one second tone includes a firstpattern of tones and a second pattern of tones transmittedsimultaneously, the first pattern being transmitted by a first node andthe second pattern being transmitted by a second node.
 9. The method ofclaim 8, wherein the first pattern is different from the second pattern.10. A wireless network, comprising: a receiver node that includes: anarrangement to receive a plurality of tones each at a predefinedfrequency; an energy storage arrangement; and a control arrangement tooperate the receiver node in a sleep mode to conserve energy, whereinthe receiver node is configured to periodically wake up from the sleepmode to listen for a wakeup tone, and upon receiving the wakeup tone,listening for at least one second tone, the at least one second tonebeing one of (i) a tone in a frequency different from the wakeup toneand (ii) a pattern of tones in at least one frequency different from thewakeup tone.
 11. The wireless network of claim 10, wherein the receivernode further includes an arrangement to perform an action based on theat least one second tone.
 12. The wireless network of claim 11, whereinthe receiver node includes at least one of a sensor and an actuator. 13.The wireless network of claim 10, further comprising: at least onetransmitter node to transmit the wakeup tone and the at least one secondtone.
 14. The wireless network of claim 10, wherein the at least onetransmitter node includes at least two transmitter nodes, at least oneof which transmits the wakeup tone, and each of which simultaneouslytransmit at least one further tone distinct from one another tocollectively form the at least one second tone received by the receivernode.
 15. The wireless network of claim 14, wherein the at least twotransmitter nodes include a first transmitter node that transmits the atleast one further tone as a single tone at a first predefined frequency,and a second transmitter node that transmits the at least one furthertone as a single tone at a second predefined frequency different fromthe first predefined frequency.
 16. The wireless network of claim 14,wherein the at least two transmitter nodes include a first transmitternode that transmits the at least one further tone as plurality of tonesin a first pattern, and a second transmitter node that transmits the atleast one further tone as a plurality of tones in a second patterndifferent from the first pattern.
 17. A wireless node, comprising: apower storage arrangement; and an arrangement to receive a plurality oftones each at a predefined frequency, wherein the wireless node isconfigured to periodically listen for a wakeup tone, and upon receivingthe wakeup tone, listening for at least one second tone, the at leastone second tone being one of (i) a tone in a frequency different fromthe wakeup tone and (ii) a pattern of tones that includes at least onefrequency different from the wakeup tone.
 18. The wireless node of claim17, further comprising: an arrangement to perform an action based on theat least one second tone.
 19. The wireless node of claim 18, wherein theat least one second tone includes a first tone and a second tonetransmitted simultaneously, the first tone being transmitted by a firstnode and the second tone being transmitted by a second node.
 20. Thewireless node of claim 18, wherein the at least one second tone includesa first pattern of tones and a second pattern of tones transmittedsimultaneously, the first pattern being transmitted by a first node andthe second pattern being transmitted by a second node.